Mitochondrial pH monitored by a new engineered green fluorescent protein mutant

J Biol Chem. 2004 Mar 19;279(12):11521-9. doi: 10.1074/jbc.M306766200. Epub 2003 Dec 30.


We here describe a new molecularly engineered green fluorescent protein chimera that shows a high sensitivity to pH in the alkaline range. This probe was named mtAlpHi, for mitochondrial alkaline pH indicator, and possesses several key properties that render it optimal for studying the dynamics of mitochondrial matrix pH, e.g. it has an apparent pK(a) (pK(a)') around 8.5, it shows reversible and large changes in fluorescence in response to changes in pH (both in vitro and in intact cells), and it is selectively targeted to the mitochondrial matrix. Using mtAlpHi we could monitor pH changes that occur in the mitochondrial matrix in a variety of situations, e.g. treatment with uncouplers or Ca(2+) ionophores, addition of drugs that interfere with ATP synthesis or electron flow in the respiratory chain, weak bases or acids, and receptor activation. We observed heterogeneous pH increases in the mitochondrial matrix during Ca(2+) accumulation by this organelle. Finally, we demonstrate that Ca(2+) mobilization from internal stores induced by ionomycin and A23187 cause a dramatic acidification of the mitochondrial matrix.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chromatography, Affinity
  • Green Fluorescent Proteins
  • HeLa Cells
  • Humans
  • Hydrogen-Ion Concentration*
  • Luminescent Proteins / genetics*
  • Mitochondria / chemistry*
  • Mutation*


  • Luminescent Proteins
  • Green Fluorescent Proteins

Grant support